The technique of transcutaneously measuring a blood gas parameter by arranging an electrochemical measuring electrode device on a skin surface part of a test person or a patient, is well-known in the art. The measurement is conventionally carried out in accordance with well-known measuring principles, such as the polarographic measuring principle or the potentiometric measuring principle.
In accordance with the potentiometric measuring principle, the blood gas parameter to be measured is the partial pressure of a gas which in an aqueous solution generates an acid or a base. Conventionally, an electrochemical measuring electrode device is employed which, in accordance with the Stow-Severinghaus principle, comprises a potentiometric electrode system including a pH-electrode and a reference electrode, and an electrolyte solution which communicates with the electrode system.
Correspondingly, in accordance with the polarographic measuring principle, the blood gas parameter to be measured is the partial pressure of oxygen. Conventionally, an electrochemical measuring electrode device is employed which, in accordance with the Clark measuring principle, comprises a polarographic electrode system including a cathode and an anode, and an electrolyte solution which communicates with the electrode system.
In operation of a Stow-Severinghaus electrode device for potentiometrically measuring the partial pressure of gas which in an aqueous solution generates an acid or a base, especially carbon dioxide, the gas in question permeates into the electrolyte solution and is dissolved therein, thereby causing a shift of pH, e.g.: EQU CO.sub.2 +H.sub.2 O.revreaction.H.sub.2 CO.sub.3 EQU H.sub.2 CO.sub.3 .revreaction.H.sup.+ +HCO.sub.3.sup.-.
Correspondingly, in operation of a Clark electrode device, e.g. when measuring the partial pressure of O.sub.2, the gas to be measured permeates into the electrolyte solution and is reduced at the cathode, i.e. the gas in question is consumed by the polarographic electrode system, i.e.: EQU O.sub.2 +2H.sup.+ +4e.sup.- .fwdarw.2OH.sup.-.
Furthermore, the technique of sensing a bioelectrical signal is well-known in the art. Conventionally, the bioelectrical signal is sensed by means of two or more electrodes which are arranged in contact with respective skin surface parts of the test person or patient and by detecting the voltage variation across the bioelectrical signal sensing electrodes. The bioelectrical signal normally represents the respiration rate, the heart rate, the ECG (Electrocardiography), or the EEG (Electroencephalography) of the test person or the patient.
Since a very important and extensive application of the electrochemical measuring electrode devices for transcutaneously measuring a blood gas parameter and of the bioelectrical signal sensing electrodes is the supervision of newborn or even prematurely born infants, there has been a need for extremely small, compact and light-weight constructions of electrochemical measuring electrode devices and of bioelectrical signal sensing electrodes, yet providing extremely reliable and accurate measuring results as to the blood gas parameter to be measured and the bioelectrical signal to be sensed, respectively. In an attempt to obtain an even higher degree of compactness it has been suggested to arrange an electrochemical measuring electrode device and a bioelectrical signal sensing electrode in a single housing, vide e.g. German patent specification DE-OS No. 29 30 663, however comprising separate electrochemical measuring components and bioelectrical signal sensing components.
Furthermore, it has been suggested to employ an electrochemical measuring electrode device comprising a separate metal component of an annular configuration surrounding the electrodes and serving the purpose of thermostatically heating the skin surface part of the test person or patient and further serving as a bioelectrical signal sensing electrode, vide e.g. published European patent application, publication number 0 071 980. Whereas the above integrally housed electrochemical measuring electrode device and bioelectrical signal sensing electrode to no substantial extent provide a reduction of the overall size and weight of the transcutaneously, blood gas parameter measuring and bioelectrical signal sensing equipment to be arranged on a newborn or prematurely born infant, as the total number of components and the size thereof is basically identical to the total number of components of identical size of a discrete electrochemical measuring electrode device and of a discrete bioelectrical signal sensing electrode, the above combined construction, in which the separate metal component is employed as the bioelectrical sensing electrode, suffers from an inherent conflict, as, on the one hand, the separate metal component has to be arranged in intimate contact with the skin surface part of the person or patient to be supervised in order to provide maximum transmission of heat from the thermostatically heated metal component to the skin surface part, and, on the other hand, the bioelectrical signal sensing electrode, as is well known in the art, preferably is arranged recessed in relation to the skin surface part of the patient in order to make the bioelectrical signal sensing procedure less sensitive to incidental motions of the patient as is described in reference 1.
Therefore, there is a need for an electrode device for transcutaneously measuring a blood gas parameter and for sensing a bioelectrical signal, which electrode device provides a mroe compact and lightweight construction than an assembly of a discrete, electrochemical measuring electrode device and a discrete, bioelectrical signal sensing electrode without introducing limitations as to its measuring accuracy and measuring reliability as compared to the discrete, electrochemical measuring electrode device and the discrete bioelectrical signal sensing electrodes.